Novel Synthesis of Polycarbazole–Gold Nanocomposite

A polycarbazole–gold nanocomposite is synthesized based on two polymerization techniques, i.e., emulsion and interfacial using aqueous gold chloride and non‐aqueous carbazole monomer solutions. Use of gold chloride as an oxidant for carbazole not only provides a new chemical synthesis for polycarbazole conducting polymer but also allows the formation of conducting nanocomposite in one simple step. Polymerization of carbazole and further growth of the polymer along with gold nanoparticles are governed by the redox reaction between carbazole and Au cations. Two different morphologies of polymers and two different sizes (with narrow size distribution) of gold nanoparticles are obtained depending on the polymerization routes. Structural and thermal properties of the nanocomposites are studied using SEM/TEM, FT‐IR, XRD, and TGA. XRD of nanocomposites depicts the amorphous nature of the polymer and the highly phase selective crystalline nature of gold. Nanocomposites with improved properties show better dispersion in common organic solvents and potential for various technological applications.

     

Nature of dynamic gradients,glass formation,and collective effects in ultrathin freestanding films

Molecular, polymeric, colloidal, and other classes of liquids can exhibit very large, spatially heterogeneous alterations of their dynamics and glass transition temperature when confined to nanoscale domains. Considerable progress has been made in understanding the related problem of near-interface relaxation and diffusion in thick films. However, the origin of “nanoconfinement effects” on the glassy dynamics of thin films, where gradients from different interfaces interact and genuine collective finite size effects may emerge, remains a longstanding open question. Here, we combine molecular dynamics simulations, probing 5 decades of relaxation, and the Elastically Cooperative Nonlinear Langevin Equation (ECNLE) theory, addressing 14 decades in timescale, to establish a microscopic and mechanistic understanding of the key features of altered dynamics in freestanding films spanning the full range from ultrathin to thick films. Simulations and theory are in qualitative and near-quantitative agreement without use of any adjustable parameters. For films of intermediate thickness, the dynamical behavior is well predicted to leading order using a simple linear superposition of thick-film exponential barrier gradients, including a remarkable suppression and flattening of various dynamical gradients in thin films. However, in sufficiently thin films the superposition approximation breaks down due to the emergence of genuine finite size confinement effects. ECNLE theory extended to treat thin films captures the phenomenology found in simulation, without invocation of any critical-like phenomena, on the basis of interface-nucleated gradients of local caging constraints, combined with interfacial and finite size-induced alterations of the collective elastic component of the structural relaxation process.

Spatially heterogeneous dynamics in glass-forming liquids confined to nanoscale domains (1–7) play a major role in determining the properties of molecular, polymeric, colloidal, and other glass-forming materials (8), including thin films of polymers (9, 10) and small molecules (11–15), small-molecule liquids in porous media (2, 4, 16, 17), semicrystalline polymers (18, 19), polymer nanocomposites (20–22), ionomers (23–25), self-assembled block and layered (26–33) copolymers, and vapor-deposited ultrastable molecular glasses (34–36). Intense interest in this problem over the last 30 y has also been motivated by the expectation that its understanding could reveal key insights concerning the mechanism of the bulk glass transition.Considerable progress has been made for near-interface altered dynamics in thick films, as recently critically reviewed (1). Large amplitude gradients of the structural relaxation time, τ(z,T), converge to the bulk value, τ_bulk(T), in an intriguing double-exponential manner with distance, z, from a solid or vapor interface (13, 37–42). This implies that the corresponding effective activation barrier, F_total(z,T,H) (where H is film thickness), varies exponentially with z, as does the glass transition temperature, T_g (37). Thus the fractional reduction in activation barrier, ε(z,H), obeys the equation ε(z,H)≡1−Ftotal(z,T,H)/Ftotal,bulk(T)=ε0⁡exp(−z/ξF), where F_total,bulk(T) is the bulk temperature-dependent barrier and ξ_F a length scale of modest magnitude. Although the gradient of reduction in absolute activation barriers becomes stronger with cooling, the amplitude of the fractional reduction of the barrier gradient, quantified by ε₀, and the range ξ_F of this gradient, exhibit a weak or absent temperature dependence at the lowest temperatures accessed by simulations (typically with the strength of temperature dependence of ξ_F decreasing rather than increasing on cooling), which extend to relaxation timescales of order 10⁵ ps. This finding raises questions regarding the relevance of critical-phenomena–like ideas for nanoconfinement effects (1). Partially due to this temperature invariance, coarse-grained and all-atom simulations (1, 37, 42, 43) have found a striking empirical fractional power law decoupling relation between τ(z,T) and τ_bulk(T):τ(T,z)τbulk(T)∝(τbulk(T))−ε(z).[1]Recent theoretical analysis suggests (44) that this behavior is consistent with a number of experimental data sets as well (45, 46). Eq. 1 also corresponds to a remarkable factorization of the temperature and spatial location dependences of the barrier:Ftotal(z,T)=[1−ε(z)]Ftotal,bulk(T).[2]This finding indicates that the activation barrier for near-interface relaxation can be factored into two contributions: a z-dependent, but T-independent, “decoupling exponent,” ε(z), and a temperature-dependent, but position-insensitive, bulk activation barrier, F_total,bulk(T). Eq. 2 further emphasizes that ε(z) is equivalent to an effective fractional barrier reduction factor (for a vapor interface), 1−Ftotal(z,T,H)/Ftotal,bulk(T), that can be extracted from relaxation data.In contrast, the origin of “nanoconfinement effects” in thin films, and how much of the rich thick-film physics survives when dynamic gradients from two interfaces overlap, is not well understood. The distinct theoretical efforts for aspects of the thick-film phenomenology (44, 47–50) mostly assume an additive summation of one-interface effects in thin films, thereby ignoring possibly crucial cooperative and whole film finite size confinement effects. If the latter involve phase-transition–like physics as per recent speculations (14, 51), one can ask the following: do new length scales emerge that might be truncated by finite film size? Alternatively, does ultrathin film phenomenology arise from a combination of two-interface superposition of the thick-film gradient physics and noncritical cooperative effects, perhaps in a property-, temperature-, and/or thickness-dependent manner?Here, we answer these questions and establish a mechanistic understanding of thin-film dynamics for the simplest and most universal case: a symmetric freestanding film with two vapor interfaces. We focus on small molecules (modeled theoretically as spheres) and low to medium molecular weight unentangled polymers, which empirically exhibit quite similar alterations in dynamics under “nanoconfinement.” We do not address anomalous phenomena [e.g., much longer gradient ranges (29), sporadic observation of two distinct glass transition temperatures (52, 53)] that are sometimes reported in experiments with very high molecular weight polymers and which may be associated with poorly understood chain connectivity effects that are distinct from general glass formation physics (54–56).We employ a combination of molecular dynamics simulations with a zero-parameter extension to thin films of the Elastically Cooperative Nonlinear Langevin Equation (ECNLE) theory (57, 58). This theory has previously been shown to predict well both bulk activated relaxation over up to 14 decades (44–46) and the full single-gradient phenomenology in thick films (1). Here, we extend this theory to treat films of finite thickness, accounting for coupled interface and geometric confinement effects. We compare predictions of ECNLE theory to our previously reported (37, 43) and new simulations, which focus on translational dynamics of films comprised of a standard Kremer–Grest-like bead-spring polymer model (see SI Appendix). These simulations cover a wide range of film thicknesses (H, from 4 to over 90 segment diameters σ) and extend to low temperatures where the bulk alpha time is ∼0.1 μs (10⁵ Lennard Jones time units τ_LJ).The generalized ECNLE theory is found to be in agreement with simulation for all levels of nanoconfinement. We emphasize that this theory does not a priori assume any of the empirically established behaviors discovered using simulation (e.g., fractional power law decoupling, double-exponential barrier gradient, gradient flattening) but rather predicts these phenomena based upon interfacial modifications of the two coupled contributions to the underlying activation barrier– local caging constraints and a long-ranged collective elastic field. It is notable that this strong agreement is found despite the fact the dynamical ideas are approximate, and a simple hard sphere fluid model is employed in contrast to the bead-spring polymers employed in simulation. The basic unit of length in simulation (bead size σ) and theory (hard sphere diameter d) are expected to be proportional to within a prefactor of order unity, which we neglect in making comparisons.As an empirical matter, we find from simulation that many features of thin-film behavior can be described to leading order by a linear superposition of the thick-film gradients in activation barrier, that is:ε(z,H)=1−Ftotal(z,T,H)/Ftotal,bulk(T)≈ε0[exp(−z/ξF)+exp(−(H−z)/ξF)],[3]where the intrinsic decay length ξ_F is unaltered from its thick-film value and where ε₀ is a constant that, in the hypothesis of literal gradient additivity, is invariant to temperature and film thickness. We employ this functional form [originally suggested by Binder and coworkers (59)], which is based on a simple superposition of the two single-interface gradients, as a null hypothesis throughout this study: this form is what one expects if no new finite-size physics enters the thin-film problem relative to the thick film.However, we find that the superposition approximation progressively breaks down, and eventually entirely fails, in ultrathin films as a consequence of the emergence of a finite size confinement effect. The ECNLE theory predicts that this failure is not tied to a phase-transition–like mechanism but rather is a consequence of two key coupled physical effects: 1) transfer of surface-induced reduction of local caging constraints into the film, and 2) interfacial truncation and nonadditive modifications of the collective elastic contribution to the activation barrier.     

Polybenzimidazoles (PBIs) Derived from Non‐Coplanar Dibenzoic Acid Containing Imidazole (IDBA): Synthesis,Characterization and Properties

A novel non‐coplanar imidazole dibenzoic acid (IDBA) was successfully prepared, and its structure was carefully characterized by FT‐IR, NMR, MS and elemental analysis. Polybenzimidazoles (PBIs) derived from IDBA were synthesized by a conventional one‐step method in polyphosphoric acid (PPA). The obtained PBIs exhibited good organic solubility, excellent thermo‐stability and interesting optical properties. The initiation decomposition temperature for these PBIs ranged from 560–600 °C, and the 5% weight loss temperature (T₅) for all these PBIs was above 600 °C in N₂. No obvious glass transition for these PBIs was observed below 350 °C. These PBIs shows UV‐vis absorption maximum around 360–380 nm and strong photoluminescence emission (blue light) around 430–440 nm in solution, which is red‐shifted to 490–510 nm in the solid state.

     

Effects of implant surface coatings and composition on bone integration: a systematic review

Objective: The aim of the present review was to evaluate the bone integration efficacy of recently developed and marketed oral implants as well as experimental surface alterations.
Materials and methods: A PubMed search was performed for animal studies, human reports and studies presenting bone-to-implant contact percentage or data regarding mechanical testing.
Results: For recently developed and marketed oral implants, 29 publications and for experimental surface alterations 51 publications fulfilled the inclusion criteria for this review.
Conclusions: As demonstrated in the available literature dealing with recently developed and marketed oral implants, surface-roughening procedures also affect the surface chemical composition of oral implants. There is sufficient proof that surface roughening induces a safe and predictable implant-to-bone response, but it is not clear whether this effect is due to the surface roughness or to the related change in the surface composition. The review of the experimental surface alterations revealed that thin calcium phosphate (CaP) coating technology can solve the problems associated with thick CaP coatings, while they still improve implant bone integration compared with non-coated titanium implants. Nevertheless, there is a lack of human studies in which the success rate of thin CaP-coated oral implants is compared with just roughened oral implants. No unequivocal evidence is available that suggests a positive effect on the implant bone integration of peptide sequences or growth factors coated on titanium oral implants. In contrast, the available literature suggests that bone morphogenetic protein-2 coatings might even impede the magnitude of implant-to-bone response.     

The Effects of Primers and Surface Bonding Characteristics on the Adhesion of Polyurethane to Two Commonly Used Silicone Elastomers

Purpose: When restoring facial defects, maxillofacial prosthodontists and anaplastologists are often limited by material deficiencies. Silicone elastomers bonded to a polyurethane liner best satisfy the functional and esthetic requirements necessary for facial prostheses; however, patients using silicone prostheses with polyurethane liners often experience varying degrees of debonding at the polyurethane–silicone interfaces. This may result in failure of such prostheses. The purpose of this investigation was to evaluate the effects of five primers on bonding between polyurethane and two commonly used silicone elastomers. Material and Methods: Six bonding regimens were used to join polyurethane and silicone materials. Each treatment group consisted of 12 specimens. Bonding regimens included (1) a 40:60 mixture of MDX4‐4210 and Silastic Medical Adhesive Type A, in conjunction with Dow Corning 1205 primer (Udagama's technique); (2) silicone A‐2000 with Dow Corning 1205 primer; (3) silicone A‐2000 with A‐330‐G primer; (4) silicone A‐2000 with Mucopren primer; (5) silicone A‐2000 with Sofreliner T primer; and (6) silicone A‐2000 with Sofreliner MS primer. Following fabrication, specimens were attached to a universal testing machine and separated in tension at a crosshead speed of 25.4 mm/min. One examiner performed the assessment of T‐peel strength (N/mm), peak load (N), and peel distance (mm) for all specimens. Mean data were analyzed using one‐way ANOVA followed by Fisher's protected significant difference multiple comparison of the means (α= 0.05). Results: A statistically significant difference (p < 0.05) in T‐peel strength was found among specimen groups. Post hoc analysis indicated that Sofreliner MS primer (1.32 ± 0.13 N/mm) and Sofreliner T primer (1.25 ± 0.11 N/mm) increased the bond strengths significantly compared to A‐330‐G primer (0.91 ± 0.10 N/mm) and Udagama's technique (0.13 ± 0.02 N/mm). Cohesive failure between silicone A‐2000 and polyurethane liner was observed when Sofreliner MS primer and Sofreliner T were used. Conclusion: Within the limitations of this study, the use of Sofreliner MS primer and Sofreliner T primer produced significant increases in the bond strength of silicone elastomer to polyurethane liner material. Based on T‐peel strength, peel distance, and peak load data, the combination of silicone A‐2000 and Sofreliner MS primer resulted in the greatest mean bond strength for silicone‐to‐polyurethane applications.     

Characterisation and applications of microcapsules obtained by interfacial polycondensation

This review highlights the materials, mechanisms and applications of microencapsulation by interfacial polycondensation in different areas. This technology entraps active ingredients inside microcapsules/microspheres, having an average diameter ranging from nanosize to several 100?µ. Polycondensation reactions take place at the boundary of two phases to form the shells of microcapsules or matrix microspheres. The emulsion can be classified into three types: water-in-oil, oil-in-water and oil-in-oil. According to the hydrophilic–lipophilic property of core phase, different active substances, such as proteins, enzymes, insecticides, herbicides, vitamins, catalysts, drugs, essential oils, dyes and phase change materials, have been successfully incorporated into different microcapsules/microspheres. Based on the shell-forming materials, this technology is capable of preparing polyamine, polyurea, polyurethane, polythiourea, polyester, polyepoxide, polyacrylamide and polysiloxane microcapsules. Over the past two decades, microcapsules prepared by interfacial polycondensation have been widely used in carbonless paper, cosmetics, pharmacy, agriculture, energy storage/transfer, thermal insulation/regulation and information and magnetic recording.     

颗粒填充复合材料的界面层研究

运用动态力学方法研究了硅粉和Al2O3填充的环氧树脂基复合材料的力学性能，结果表明当填料含量超过20phr时，随着填料含量的增加，复合材料的玻璃化转变温度Tg逐渐移向高温区，损耗峰的半高宽度W1／2趋于增宽。当填料含量在20phr时，损耗峰的高度和半高宽度W1／2分别有一个突跃式的下降和增宽，而且Tg大于纯环氧体系。利用WLF方程对环氧复合材料的模－温度关系进行了理论推算，结果表明用WLF方程预估这类复合体系在Tg附近的模量是可行的。     

无毒催化剂催化合成外消旋聚乳酸及其在药物缓释微球中的应用

以D，L－乳酸单体为原料，使用人体营养添加剂如乳酸锌、乳酸钙，乙酸锌、硫酸锌、牛磺酸等作为无毒催化剂，通过熔融聚合直接合成低分子量的生物降解材料外消旋聚乳酸（PDLLA），粘均分子量接近4000，以PDLLA为载体，应用于制备抗菌药物环丙沙星聚乳酸微球，用DSC和SEM表征其成球性能，载药微球体外缓释半衰期为31．9h,53.2h后累积释药百分率约为84．0％，具有明显的缓释作用。     

The Complex Crystalline Structure of Polyethylene/Polycarbonate Microfibril Blends in a Secondary Flow Field

A mass of stretched molecular chains in the entire thickness direction of gas‐assisted injection molding (GAIM) composites is induced due to the redistribution and amplification of the shear flow caused by the introduction of polycarbonate (PC) microfibril under intense shear stress. In the vicinity of the PC microfibrils, stretched chains are either absorbed by PC microfibrils with a large diameter to form a transcrystallinity, or captured by ultrafine PC microfibrils to firstly form shish nuclei and finally form hybrid shish‐kebab structures. Typical shish‐kebab superstructures are formed in the zone with the absence of PC microfibrils. In summary, multi­form crystalline superstructures across the thickness direction are successfully obtained by the GAIM. Thus, this work can open a new way for the preparation of high‐performance polymer composites in industrial processing.

     

Poly(Ethylene Furanoate) along Its Life-Cycle from a Polycondensation Approach to High-Performance Yarn and Its Recyclate

We report on the pilot scale synthesis and melt spinning of poly(ethylene furanoate) (PEF), a promising bio-based fiber polymer that can heave mechanical properties in the range of commercial poly(ethylene terephthalate) (PET) fibers. Catalyst optimization and solid state polycondensation (SSP) allowed for intrinsic viscosities of PEF of up to 0.85 dL·g⁻¹. Melt-spun multifilament yarns reached a tensile strength of up to 65 cN·tex⁻¹ with an elongation of 6% and a modulus of 1370 cN·tex⁻¹. The crystallization behavior of PEF was investigated by differential scanning calorimetry (DSC) and XRD after each process step, i.e., after polymerization, SSP, melt spinning, drawing, and recycling. After SSP, the previously amorphous polymer showed a crystallinity of 47%, which was in accordance with literature. The corresponding XRD diffractograms showed signals attributable to α-PEF. Additional, clearly assignable signals at 2θ > 30° are discussed. A completely amorphous structure was observed by XRD for as-spun yarns, while a crystalline phase was detected on drawn yarns; however, it was less pronounced than for the granules and independent of the winding speed.